When dimensionally stable electrodes of the mentioned type have been used for an extended period of time, for example as anodes in an electrolysis cell for the production of chlorine and alkali metal hydroxides, the coatings are subjected to wear and damage and eventually the electrodes have to be recoated. Recoating is sometimes carried out after completely stripping off the remaining coating in a molten salt bath or by sandblasting followed by etching of the valve metal base, but advantageously in some instances the electrode surface is simply cleaned to remove loose material and foreign matter without removing adhering portions of the electrocatalytic coating, and a new removing adhering portions of the electrocatalytic coating, and a new electrocatalytic coating similar in composition to the old coating is applied over the old coating in a number of layers with drying and baking of each layer at about 300.degree. C. to 500.degree. C., as taught in U.S. Pat. No. 3,684,543. A modification in this so-called top-coating procedure claimed in USSR Patent No. 522.284 is to enrich the platinum-group metal oxide component of the new electrocatalytic coating by 10-20% compared to the old coating (eg. a RuO.sub.2 :TiO.sub.2 molar ratio of 30:70 in the old coating and 33:66 in the new coating).
This top-coating procedure has a number of advantages over methods involving stripping of the old coating. For instance, it avoids the substantial loss of weight and weakening of the valve metal base produced by the stripping and etching treatments. However, the top-coating procedure is only considered technically and economically feasible if the electrode to be recoated meets certain standards, for example the remaining coating should be uniformly distributed and should contain a minimum amount of the platinum-group metal oxide behaving as an active electrocatalyst. In practice, therefore, the electrodes to be recoated are examined to determine the amount, the uniformity and activity of the electrocatalyst and only electrodes with an appreciable quantity of remnant active coating (several grams per square meter of the electrocatalyst, calculated on a metal weight basis) in good condition are selected for top-coating and the remaining badly worn electrodes are subjected to the complete stripping and recoating procedure, despite its disadvantages.